It may be time to retire the five-second rule. A new study demonstrates that some dropped foods, such as watermelon chunks, slurp up floor bacteria almost instantly.
The study, published in Applied and Environmental Microbiology, tested gummy candies, watermelon chunks, and buttered & unbuttered bread by dropping tidbits onto several surface types that were coated with Enterobacter aerogenes -- a harmless bacteria that shares attachment characteristics with stomach-churning Salmonella.
Food was left on each surface -- stainless steel, ceramic tile, wood, and carpet -- for periods ranging from less than a second to five minutes. Afterward, the researchers measured the amount of E. aerogenes on the food.
As expected, longer contact times generally meant more bacteria on the food. But the transfer depended on other factors, too. Carpet, for instance, was less likely to transfer bacteria than the other surfaces. Gummy candies, particularly those on carpet, stayed relatively clean. But juicy watermelon chunks quickly picked up lots of bacteria from all surfaces in less than a second.
These complexities mean that the five-second rule isn't much of a rule at all.
Read an abstract of the study here: http://aem.asm.org/content/early/2016/08/15/AEM.01838-16